Method of surface treatment of metal



Jim W v H. H. HOLLOWAY 1,

- Filed 001;. 24-, 1931 I BY INVENTOR.

" ATTORNEY-5.

Patented no: 16, 1934 y 1,943,754.

UNITED STATES rrrrrrrr OFFICE Harry H. Holloway, Apollo, Pa,., assignor to Apollo Steel Company, Apollo, Pa., a corporation of Pennsylvania Apnlicatlon October 24,1931. Serial No. 570,800

5 Claims. (Cl, Mil- The present invention relates to improvements enlarged, taken through a hot metal sheet at the in the method of finishing metal, and more parinstant of contact with the water and rolls; and ticularly metal sheets, to produce what is known Fig. 3 is a view similar to Fig. 2, showing the in the art as a blue" sheet, having the surface sheet after having passed through the rolls. 515 thereof-coated with a thin layer or metal oxide In the customary method of rolling steel till of a deep blue color. sheets, the sheet bar is first hot rolled to about Steel sheets of this character are highly de- 60% of length, pickled, hot rolled to size and sirable in the manufacture of automobile bodies, gauge, and then sheared into sheets of the relocomotives, stoves, and the like, wherein the oxquired shape and dimension. m idized surface of the sheet forms an efficient They are next either box-annealed or nori555 guard against rust. malized, depending upon the desired internal Blue-annealed" or steam-blue steel sheets structure of the sheets, cooled, pickled, and then have been produced heretofore by what is cold rolled through the required number of termed the steam process, consisting in passing passes with the sheets and rolls cold and dry, to w live steam over cold rolled sheets, which. have bring them down to the exact gauge and to pro- '70 been re-heated to a certain degree, until they duce a hard smooth finish. Steel sheetsprogradually become cooled and assume a-blue color duced by this method are steel gray in color. by the iormetion or an oxide coating on the sur- In producing blue sheets of the character races thereof. described by means of my method, the above opl'he onide coating resulting from this processv erations are followed up through and including it has been found to be loosely combined with the the shearing of the sized sheets, and then they sheet, causing the same to crack and flake or are pickled in the usual solution and by any chin bill when the sheet is subjected to severe suitable process. bending onerationsthus rendering the sheet im- The sheets are then heated, preferably in a practicable for many die-pressed products. continuous furnace or by boxannealing, until 80 also, the cost of such sheets is materially in they are raised to a temperature of 5004500 creased, due to the re heating operation and the degrees Fahrenheit. This temperature range lenuth of time required to complete the process. may vary for various alloy sheets, depending My invention contemplates the production of upon the nature of the alloy. For example, for m a sheet of the character designated, having an the usual steel automobile body sheets, it has 85 oxidized surface formed in the final rolling or been found that the best temperature is 1200 finishing operation by reducing the hot unfin degrees Fahrenheit to give the most satisfactory ished sheet between cold polished rolls, over results. which Welt?! is wnllmuhlly p hereby form- The hot sheets are then taken to a finish mill me a O iole layer ich i b chemically d comprising a pair of cold polished rolls 2, set to mechanically Co b d h the metal of the accurately reduce the sheets to the required Shela? m Such a manner a the metal becomes gauge. The said rolls are flooded with water, in

m infused or impregnated with the said the manner shown, by means of perforated pipes M 3 or other suitable means, for completely covergfig tgfizgi fg mffi g figg gfi g gg ing the roll surfaces with the water, which is tively secures the oxide layer against removal preferably cold when the sheet is bent, pressed or otherwise Each Sheet T xsprefqably aerated Worked. In addition, the resulting product has mg otherwlse exposmg the same to W ii"; high fi i h m u ssfull masks my pheric action before passing to the rolls 2, to let) moves urfaceimperfgcflgng and one m is free the surfaces thereof from foreign matter produced without appreciably changing the mand to tend to equalize the surface temperatures ternal structure of the sheet. on both sides of the sheet. I

\ In the tlliilWlllE, which illustrates diauraat- The heet A i hen d awn th h th m ieally the apparatus and operation or mytlnvenw rolls 2 a e sa d p e d temp ra u chm; The intense heat of the sheet converts the water Win. 1 is an end view of a pair oi cold finish into steam at the instant of contact, which steam inn rolls, showing the application oi Water is confined in the minutespace between the thereto; I rolls and the surfaces of the sheet. The oxygen H0 i a is a iraanientary sectional view greatly, in the steam chemically combines with the metal of the sheet to produce a film or layer of oxide 4 covering the surfaces of the sheet.

Prior to its passage through the rolls 2, the sheet ordinarily has imperfect surfaces, due to the presence of a large number of minute defects or abrasions such as blow holes, pin holes, scratches, pits, etc., resulting from the reducing operations. Such imperfections are indicated at 5 in Fig. 2, greatly enlarged.

At the instant of contact of the hot sheet with the water and rolls, the film or layers of oxide 4 produced will be in such a state of fluidity that they will fill the imperfections or openings 5, as indicated in Fig. 2.

The instantaneous mechanical action or pressure of the rolls 2 operates to roll the oxide layers 4 into the surfaces of the sheet A. Due to the reduction of the sheet A in passing through therolls, the surfaces of the sheet and the oxide layers will be highly compressed and rolled together, thereby forming a mechanical combination between the sheet and the oxide layers by the deformation and depression of the oxide-containing imperfections or openings 5, as indicated in Fig. 3.

The hard smooth surfaces of the finishing rolls will produce a continuous smooth finish on the oxide coatings or layers which will be practically free from abrasions of the character described and for which sheets may be rejected as imperfect. In addition, when the sheet has cooled, the oxide will take on a dark blue color.

Actual tests have shown that the oxide coatings so formed will not crack or fiake off when the sheet is subjected to the most severe bending actions, as, for example, bending the sheet back upon itself. Also, steel sheets produced by means of my process are being satisfactorily used in the production of die-pressed automobile bodies, or other deformed shapes.

Thus, it will be seen that by means of my method, a blue" sheet may be produced having all the desirable characteristics of the old blueannealed sheet, with the added property that the oxide coating will not come off during the working of the sheet. And, further, the reheating operation of the "steam-blue process -is dispensed with, thereby decreasing the time element as well as the actual cost of heating. Time is also saved, due to the fact that it is not necessary to cool the sheets as in the old process before cold rolling and finishing.

An important application of my invention resides in the use of the process in re-claiming and perfecting cold rolled sheets which have been produced under the old method and have been rejected for surface defects remaining after having passed through the final cold rolling operation.

The, sheets are heated to the desired temperature within the prescribed range, and then passed through the cold wet rolls as stated, to apply the oxide coating and produce blue" sheets wherein the surface defects are successfully masked or removed, due to the combined action hereinbefore described.

I claim:

1. The final step in the method of finishing steel sheets consisting'in applying an oxidizing blue finish to the opposite sides of thin previously densified steel sheets by re-heating the sheet, then passing it between a pair of polished rolls each supplied with an individual water film, and effecting instantaneous oxidation and compression of the resulting oxide upon and into opposite sides of the sheet throughout their surface areas.

2. The final step in the method of finishing 100 steel sheets consisting in applying an oxidizing blue finish to the opposite sides of thin previously densified steel sheets by re-heating the sheet, then passing it between a pair of polished rolls each supplied with an individual water film, and 1(5 effecting instantaneous oxidation and compression of the resulting oxide upon and into the plane and other surfaces on opposite sides of the sheet throughout their surface areas.

3. The final step in the method of finishing 110 steel sheets which consists in forming a permanent blue oxide coating on the surfaces thereof by passing said sheets while heated, be-' tween a pair of cold polished rolls each supplied with a water film. 1

4. The method of reclaiming and refinishing cold rolled steel sheets having surface defects which consists in reheating the sheet, and forming a permanent blue oxide coating on the surfaces thereof by passing said sheet between a pair of cold polished rolls each supplied with a water film.

5. As an article of manufacture, a steel sheet, the surfaces of which contain a permanent blue oxide coating formed by subjecting the sheet 125 while heated to the simultaneous action of cold polished rolls and water.

HARRY H. HOLLOWAY. 

